The invention relates to a method for calibrating a rotatable and pivotable technical stage device.
EP 0 814 344 A2 describes a device and a method for a lighting equipment tracking a moving target. EP 1 385 335 A1 and WO 2007/100258 A1 describe methods relating to fixedly arranged projectors.
In particular for the lighting of stages in the field of theatre and event technology, but also for other uses, technical stage devices are known which are arranged rotatably and/or pivotably along two axes above a ground.
These devices may in particular be spotlights or cameras. Corresponding spotlights are for example known as moving heads or moving-head spotlights, while corresponding cameras are known as pan-tilt cameras or pan-tilt-zoom cameras.
The two axes are a pivot axis extending parallel to the ground (usually referred to as tilt axis) and a rotational axis extending normal to the ground (usually referred to as pan axis).
Such devices, in particular spotlights and cameras, are rotatable about the pan axis by usually 540°, i.e. one and a half turns, and pivotable about the tilt axis by usually 180° to 240°.
Thus, each point on the sphere sector covered can be reached in two ways: either with a certain pan value X and tilt value Y or with a pan value of X+180° rotated away and with the tilt value mirrored along the vertical axis (so-called tilt flip). If, for example, a corresponding spotlight projects a pattern, it would be visible on the stage normally in the first case and upside down in the second one.
With such a device that is fixedly or moveably mounted on the ceiling or a stage construction, e.g. a spotlight or camera, preferably each point on the stage may be reached by setting the pan and tilt values. A spotlight creates an illuminated, preferably elliptical, area on the ground by means of a directed cone of light. A camera captures a certain observation area of the stage.
In order to set up such moveable devices for the computer-aided and preferably automatic lighting or capturing of the performers on stage, the devices have to be calibrated with regard to their position and control values.
In particular, the position of the devices has to be known in absolute coordinates. In addition, it has to be known which control values of the protocol used lead to the desired rotation of the device, wherein the pan and tilt values of the device must be mapped to the most often used DMX protocol. In practice, however, several problems arise during calibration.
First, it has to be determined at which point in the three-dimensional space the device is located (x, y and z coordinates). This is usually done by measuring the stage space and the position of the technical stage devices, as well as by generating a three-dimensional model with the help of a computer.
This is cumbersome and prone to errors; in most cases, it is not possible to measure the exact position of the devices correctly. There is also a risk of an intentional or unintentional change of the position of the device between the time of the measurement and the time of the performance.
Furthermore, the relationship between the digital pan and tilt values used to control the device and the resulting changes in the absolute angular coordinates on the stage must be established. In other words, it has to be determined what pan and tilt values are required to achieve a certain angular change in the area on stage that is illuminated by the spotlight or observed by the camera.
This mapping assignment is also usually generated from the computer-generated 3D model; hence, the same inaccuracies may occur.
A reliable assignment of the computer-generated model to the real conditions in the stage space is not possible. Lastly, an unequivocal localisation of the technical stage devices also requires the determination of the rotation, i.e. the orientation of the technical stage device. Here, too, the problem arises that the computer-generated model generally does not correspond to the actual conditions.